How to use the Trapezoid Area Calculator
Enter the two parallel sides and the height between them, all in the same unit. The area comes back in square units.
Worked example
A garden bed has parallel sides of 6 m and 10 m and is 4 m deep. The average of the parallel sides is (6 + 10) ÷ 2 = 8, and 8 × 4 = 32 m². That figure tells you how much soil, turf or paving to order.
Which sides are the bases
The two bases are the sides that run parallel to each other. The height is the straight, perpendicular distance between them. If you only know the slanted sides, measure straight across instead, or split the shape into a rectangle and two triangles and add their areas.
The formula
Area = (a + b) ÷ 2 × h
Examples
- Sides 6 and 10, height 10
Area: 80
- Sides 4.5 and 9, height 3
Area: 20.25
- Sides 12 and 20, height 7
Area: 112
Limitations and assumptions
Use the perpendicular height between the parallel sides, not the length of a slanted side.
Frequently asked questions
What is the trapezoid area formula?
Area = ½ × (a + b) × h.
Which sides are the bases?
The two parallel sides.
What is the height?
The perpendicular distance between the bases, not the slanted side.
Is a parallelogram a trapezoid?
When a = b the formula reduces to base × height.